Olefinically unsaturated carboxylic acids include rosin acids and fatty acids. These acids are a common additive to rubber compounds. When converted to a more saturated form, the more saturated fatty acids are easier to handle and the more saturated rosin acids render the rubber to which they are added more tacky. One way to reduce the level of unsaturation in an unsaturated carboxylic acid is to heat the unsaturated acid to a high temperature and high pressure in the presence of hydrogen. Obviously, the use of such high reaction conditions significantly contribute to increasing the cost of producing such acids with reduced unsaturation.